This invention relates to a process for the removal of H.sub.2 S-containing sour gases from gaseous mixtures containing carbon monoxide and at least one heavy metal carbonyl, and in particular to a process comprising scrubbing said gaseous mixture under superatmospheric pressure at a temperature below 0.degree. C. with a scrubbing medium capable of absorbing said H.sub.2 S-containing sour gas, heating resultant loaded scrubbing medium in a heat exchanger, and expanding resultant loaded scrubbing medium to liberate the H.sub.2 S-containing sour gas and regenerate the scrubbing agent, wherein in the absence of a preventive measure, said heat exchanger is fouled by heavy metal sulfides.
It is known that the fouling of apparatus with metallic sulfides during the processing of CO-containing cracked gases produced by the gasification of solid or liquid fuels with steam and oxygen under elevated pressure and temperature is a severe problem. It has also been recognized that this problem is, in the final analysis, due to gaseous metal carbonyls formed during the course of processing of the cracked gases, which carbonyls have the tendency to form sulfides with sulfur compounds present in the cracked gas or in other compounds used in the process; these sulfides, in turn, are deposited on certain parts of the apparatus and clog same during the course of time.
In the production of industrial gases, the acidic components, such as, for example, CO.sub.2, H.sub.2 S, and COS, and collectively termed sour gas must be removed from the gaseous mixtures. This is advantageously accomplished by scrubbing with physical scrubbing media, e.g., alcohols, glycols, or ethers. The methanol scrubbing process proved to be especially advantageous, wherein the sour gas components are separated at temperatures of down to below -70.degree. C. and under high pressure (up to 80 bar). For regeneration, the scrubbing medium, after absorption of the sour gases and the methanol soluble metal carbonyls, is expanded, treated with stripping gas, or heated in heat exchangers. During this procedure, the metal carbonyls decompose into CO and reactive heavy metals, the latter, in turn, forming metallic sulfides with the H.sub.2 S present, whereby obstructions occur at various locations in the apparatus.
To prevent such fouling of the apparatus, U.S. Pat. No. 4,142,875 for example, proposes to precipitate heavy metal compounds, which would normally cake in the degasification column, prior to entrance of the solution into this column by heating at least part of the scrubbing solution to 70.degree.-250.degree. C. under a pressure higher than the vapor pressure of the scrubbing liquid and with a residence time of at least 0.25 hour, in a preliminary reactor which can be filled with a packing material.
The deposits, however, can also occur within the heat exchangers used for heating the scrubbing medium from a temperature of, e.g., -40.degree. to +90.degree. C., especially -20.degree. to +80.degree. C. prior expansion. The latter occurrence is especially disadvantageous, since the removal of these deposits from the heat exchangers is very difficult.